EUV light generation utilizing a plasma formed from metals such as tin in the form of a target for plasma initiation by irradiation of the target, e.g., a droplet of liquid tin in a laser produced plasma EUV light generator or in a discharged produced deep plasma focus produced plasma using, e.g., tin, as the plasma source have been proposed in the art. A problem with tin in such applications has been the removal of plasma produced debris from optical surfaces in the EUV light source production chamber. Such optical surfaces may be, e.g., reflective surfaces, e.g., in a collector, e.g., using mutilayer mirrors with many stacked layers forming the reflecting optic or a few layers forming a grazing angle of incidence reflecting surface or may be transmitting surfaces, e.g., lenses and windows used, e.g., to direct and/or focus a laser beam(s) on the plasma production target for LPP or for various metrology uses. Lithium, tin and Xenon, among other elements have been proposed as plasma production source materials for plasma produced EUV light generation, both of the discharged produced plasma (“DPP”) variety, otherwise sometimes referred to as Dense Plasma Focus (“DPF”P or Dense Plasma Pinch (“DPP”) or the Laser Produced Plasma (“LPP”) variety. One of the troubling aspects of tin as a target according to the art is the perceived inability to remove tin from optical elements critical to the operation of the DPP or LPP apparatus for producing EUV light, e.g., the primary collector mirror in either a DPP or LPP system, or from such optics as windows used, e.g., for metrology and/or lenses used for, e.g., metrology and/or focusing or directing of the laser light pulses to the plasma initiation site for LPP. For lithium as discussed, e.g., in the above referenced co-pending applications, several strategies for lithium debris removal exist, e.g., simply heating the reflective surface of the mirror or other optical element to, e.g., about 450-500° C. and evaporate the lithium from the mirror surface.
Tin halides and halides of other possible target materials have been proposed as the source of the target material as discussed in WO03/094581A1, entitled METHOD OF GENERATION F EXTREME ULTRAVIOLET RADIATION, published on Nov. 13, 2003.
Applicants propose various solutions to the difficulties in debris mitigation with such targets as tin.